ASTM D6701 Standard Test Method for Determining Water Vapor Transmission Rates Through Nonwoven and Plastic Barriers
What is ASTM D6701?
ASTM D6701 is a standard test method that determines the transmission rate of water vapor through barrier materials. Firstly, this method is used for plastic films, polymer barriers, nonwoven fabrics, and nonwoven materials with a film coating. Secondly, the test method measures the water vapor transmission rate (WVTR) and water vapor permeance of materials under defined test conditions. The obtained results indicate the ability of the material’s barrier properties to resist the passage of water vapor, thereby affecting the storage, stability, and comfort of products. During the experiment, the test specimen is placed between the wet and dry chambers of a diffusion cell to allow water vapor to pass through the specimen. In general, the method specifies WVTR rates of 500 to 100,000 g/(m²·day) and specimen thickness of up to 3 mm. Manufacturers and laboratories can use this method to evaluate the comparative barrier properties of materials and check materials’ compliance with specified requirements.
Get Certified ASTM D6701 Testing to Evaluate the Performance of Barrier Products
The performance of packaging, protective clothing, and other barrier products can be compromised by moisture in various stages of their service life. ASTM D6701 testing enables manufacturers to determine the amount of water vapor transmitted through a given material at a specific time interval under a controlled environment. In addition, an experienced laboratory can examine the specimens, identify the rate of moisture transfer, and provide the results as per the standard. The test method should be performed in accordance with ASTM D6701 and include additional procedures and specific conditions for sampling and testing.
What is the Scope of ASTM D6701?
ASTM D6701 is a standard test method that covers the measurement of water vapor transmission through nonwoven and plastic barrier materials. In addition, the method helps to determine both water vapor transmission rate and water vapor permeance under specified conditions. Moreover, the method applies to films, single- or multilayer polymer barriers, nonwoven fabrics, and film-coated nonwovens up to 3 mm thick.
Material type: Plastic films, synthetic or natural polymer barriers, nonwoven fabrics, and film-coated nonwoven materials.
Purpose: The method evaluates the movement of water vapor through a barrier material.
Properties evaluated: Water vapor transmission rate (WVTR) and water vapor permeance.
Testing method: A diffusion cell with wet and dry sides analyzes water vapor passing through the specimen.
Result: A numerical WVTR value and water vapor permeance, as applicable.
Test limitation: The method covers a stated transmission-rate range and material thickness. Results depend on the specified test conditions and specimen suitability.
Methodology: The specimen forms a barrier between the wet and dry sides of the test cell, and the system measures vapor transmission.
ASTM D6701 testing assists manufacturers in determining the performance characteristics of different barrier materials. The information obtained from the study aids material selection and supports comparative analysis of films at a given set of standard test conditions. Laboratories can use the results to evaluate the barrier attributes of a given material or assess its compliance against specific requirements. The Standard method:
Supports material selection for moisture protection based on the water vapor transmission rates of different barrier films.
Helps to enhance product development by identifying materials appropriate for a given moisture control need.
Interprets water vapor transmission data to understand the behavior of nonwoven and plastic barriers.
Evaluates whether packaging materials offer the desired level of moisture protection for a specific product.
Helps to compare the performance attributes of single- and multilayer materials to determine the differences in their performance characteristics.
Establishes whether the values obtained during a test meet the requirements set for a particular application or material.
Why is ASTM D6701 Important?
Water vapor can impact a product’s shelf life, stability, breathability, and wearing comfort. ASTM D6701 offers a standard test method for water vapor transmission through suitable barrier materials. The results of the test enable manufacturers to evaluate materials and get to know what they are made of. Buyers and sellers can apply the standard in testing practice to establish a reference for comparison, including agreement of sampling procedure and test conditions.
How does water vapor transmission influence the barrier performance?
A higher water vapor transmission rate indicates the amount of water vapor that passes through a unit area of film or sheet of material per unit of time. This may be relevant in the case where moisture protection is required. The rate at which water vapor travels through a material depends on its purpose and application.
What is the difference between WVTR and water vapor permeance?
While WVTR defines the quantity of water vapor that passes through a unit area, water vapor permeance determines the transmission rate relative to the vapor pressure. ASTM D6701 offers guidelines on the determination of both water vapor permeability and WVTR.
ASTM D6701 Equipment and Sample Preparation Guide
Before testing, the technician shall verify that the material is within the scope of the method and shall prepare a specimen that covers the test opening with no leakage at the edges. The equipment shall maintain the necessary wet and dry conditions for the measurement period. The test requires careful preparation to ensure relevant results for comparison.
A representative specimen of film, polymer, nonwoven fiber, or film-coated nonwoven materials within the scope of this standard.
Sample Preparation
The specimen shall be prepared and handled in accordance with the requirements of this standard. The test area shall be free of contaminants that could affect the vapor transmission rate.
Sample Dimensions
The specimen shall be prepared so that it will fit and be sealed within the diffusion cell. The technician shall refer to ASTM D6701-24 for required dimensions and specimen numbers for testing.
Instrumentation
Diffusion cell with wet and dry chambers, suitable vapor measurement system or sensor, and appropriate test-condition controls. The test apparatus shall be in accordance with the requirements of this standard.
ASTM D6701 Testing Procedures and Requirements
The technicians must ensure that a suitable specimen has been identified and a test cell is prepared correctly following the test criteria. They must ensure that the standard conditions are met. The technicians collect the required measurements and calculate or record water vapor transmission data and related values. ASTM D6701 testing procedure is as follows:
Technicians must ensure the material is a film, polymer-based barrier, nonwoven fabric, or film-coated nonwoven within the standard’s scope, and that the material thickness conforms to the standard specifications.
Prepare the specimen
Personnel must prepare a specimen under the standard’s requirements, avoiding specimen folding, tearing, or other defects that introduce errors in measurement results.
Set up diffusion cell
The technicians must ensure that the wet chamber, dry chamber, measuring diaphragm, and cell-mounting system are calibrated and ready for testing and prepare the test cell accordingly.
Mount specimen
The technicians must mount the specimen in the cell in such a way to separate the dry and wet chambers and ensure seal integrity to avoid vapor leakage.
Establish test condition
The technicians must ensure that the standard’s humidity, temperature, and other requirements are met in the test cell to ensure that the specimen is under the standard’s regulations.
Measure vapor transmission
The technicians must monitor the measuring system and record the required data for the calculation of the water vapor content transpired through the film in accordance with the standard.
Calculation and result reporting
The personnel must calculate the resultant WVTR and, if applicable, water vapor permeance from the measurements taken and compare these data to the requirements stated in the contract specification.
ASTM D6701 Testing Process and Data Collection
Technicians choose a specimen, which represents the evaluated barrier material. They should properly prepare the diffusion cell and install the specimen so that no vapor could enter or exit on its edges. After ensuring the wet and dry side of the diffusion cell are divided by the specimen, they should initiate the process of water vapor transmission through the material. During the testing, the measuring device should gather data about vapor transmission rate. Technicians should calculate the value of WVTR before determining the water vapor permeance with the set pressure difference. The technicians provide the test results with materials’ identification, test conditions, measurement data, and calculation results. Overall, they should double-check the specimen seal and test setup if they suspect an error in the measurement.
Nonwoven and plastic barrier materials evaluated for water vapor transmission rate and permeance according to ASTM D6701.
Common challenges and Troubleshooting
Several problems can arise during a water vapor transmission test. For example, if the specimen is not properly sealed, the loss of vapor from the cell will not penetrate the material. However, in case of inaccurate results, technicians first, make sure that the specimen and its location are correct, and repeat the experiment. Additionally, they check that the dry and wet side are held at the indicated conditions because differences in temperature and humidity can affect the test results. Moreover, faulty measurement systems can also cause inaccuracies, therefore, make sure to check and calibrate the equipment. Next, technicians ensure that the material is suitable for the test method and the thickness is within the specified limits. Finally, they compare results only for materials tested using the same procedure and conditions. All these steps will help laboratories to identify the cause of inaccurate findings before proceeding to the final results.
ASTM D6701 Analysis, Results and Interpretation
The standard ASTM D6701 offers the water vapor transmission rate and water vapor permeance values for the suitable barrier materials. These results help to compare materials tested at equivalent conditions. The final evaluation should consider the material’s end-use and the specifications used to define the requirements. The main points of interpretation are:
Technicians check for the higher water vapor transmission rate (WVTR) which suggests a larger amount of water vapor transferred through the material per unit area and time at the specific test conditions.
Analysts determine that materials with a lower WVTR may provide better moisture protection for the particular application, depending on the requirements.
Testing teams compare results only when the test conditions and sampling were appropriate to allow a valid comparison.
Quality control teams check water vapor permeance data if the application involves water vapor transmission in the presence of vapor pressure differential at the film’s surface.
Analysts evaluate relevant results against the specimen seal, material, and test setup conditions in order to ensure that the results aligns with the standard.
Overall, manufacturers focus on the determination of the material’s acceptance based on the relevant product specification or buyer/seller criteria.
ASTM D6701 describes a test method for determining water vapor transmission rate and water vapor permeance of nonwoven and plastic barrier materials suitable for packaging.
What materials are suitable for testing according to D6701?
ASTM D6701 covers film, single- or multilayer polymeric barriers, nonwoven fabrics, and nonwoven/film laminates up to 3 mm in thickness.
What are the units of measurement for WVTR as determined by ASTM D6701?
The standard specifies that the water vapor transmission rate shall be expressed in grams per square meter per day (g/(m²·day)).
Why is WVTR an important property for packaging materials?
WVTR is valuable information about the barrier properties of a packaging material. The results can be used by manufacturers to compare materials or evaluate a material’s ability to meet performance requirements.
Zunaira Tehseen is a scientific content specialist who bridges interdisciplinary research across biochemistry, molecular genetics, and materials science with technical content management. Leveraging expertise in bio-interface characterization, advanced materials evaluation, and AI-driven workflows, she curates, structures, and communicates complex technical data. At Matestlab, she leads content strategy and documentation for metallographic testing, mechanical characterization, and compliance with international standards such as ASTM and ISO, delivering precise, high-impact technical assets for industrial and scientific audiences. Know More
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